A memory device has the advantages of multiple operations such as storing, reading, erasing, etc., and the stored data does not disappear after power-off. Thus, a memory device has been widely used in personal computers and electronic equipment.
Generally, in the process of forming a memory device, after a floating gate structure is formed, a nitride layer is formed on the floating gate structure and serves as an etching stop layer for the subsequent contact forming process. The nitride layer is a so-called contact etching stop layer (CESL). However, the contact etching stop layer usually has defects therein and causes charge accumulation, thus affecting the device performance during the operation of the memory device.
For example, after the memory device is programmed, in a high temperature environment (in 150° C.−300° C. range), the charge stored in the floating gate moves toward the contact etching stop layer due to the charge accumulated in the contact etching stop layer, and accordingly accumulates in a region of the floating gate adjacent to the contact etching stop layer, thus generating polarization phenomenon. As a result, the amount of current flowing through the underlying channel region is decreased, and the device performance is accordingly reduced.